Interpreting complex sensory stimuli is critical for normal human functioning. Many diseases and disorders, including autism and hyperactivity, involve sensory deficits or abnormalities. These commonly include hyper- and hypo-responsiveness to different types of simple and complex stimuli. The superior colliculus, which is involved in sensing auditory, visual, and somatosensory stimuli, is thought to participate in processing complex stimuli and directing attention appropriately. While studies of visual pathways involving the superior colliculus have yielded promising results relating to sensorimotor processing and attention, these findings may be limited by focusing on the visual modality. In order to fully understand the sensorimotor processing occurring in response to complex stimuli, we must explore other sensory modalities. This proposal will explore the orienting and attentive functions controlled by the superior colliculus in relation to somatosensation using the rat vibrissa system as a model. We will investigate a putative closed sensorimotor loop which transforms sensory information into motor output with the goal of elucidating general sensorimotor transformations which generate responses to mono- and multisensory stimuli. I will also test how mechanisms regulating states of vigilance or arousal may affect this sensorimotor processing. Specific Aim I: To test the hypothesis that the tectofacial neurons are the transformer in a vibrissa sensorimotor loop. I predict that tectofacial neurons receive somatosensory input and can drive sustained firing in facial neurons. To test this I will investigate the response properties and relevant biophysical properties of identified tectofacial neurons, using both in vivo and in vitro preparations. Specific Aim II: To test the hypothesis that activation of the brainstem cholinergic system enhances the operation of the vibrissa-tectal sensorimotor loop. I predict that the cholinergic system increases the responsiveness of tectofacial neurons to somatosensory stimuli, and increases their ability to drive downstream motoneurons. I will test these predictions by activating cholinergic brainstem regions in vivo and by applying cholinergic agents in vivo and in vitro. We are investigating the role of the superior colliculus in responding appropriately to somatosensory stimuli. This study will contribute to our understanding of how people interpret and respond to simple (i.e. a pin prick) and complex (i.e. a hug from a parent) stimuli.